Scottomyzon Gibberum (Copepoda) Associated With White Sea Starfish Asterias Rubens in Spatial and Temporal Aspects - Page 01

Results and Discussion

The seasonal dynamics of the population index (prevalence, intensity and index of variation) was analysed according to the starfishes collations data, conducted during the vegetation period of 2012 and 2013.

The seasonal dynamics of the copepods S. gibberum population on starfishes A. rubens can be seen trough the indices' value on the Figure 3. 95% confidence intervals for the indices' value were calculated using Bootstrap. Through the indices' value the overlapping confidence intervals for almost the entire vegetation period can be observed. The F-test (P<0.05) for population indices shows the differences depending on the date of the sample collection.

This dynamic does not have the exact same graphic for each point, but some common features can be identified. There is a smooth decrease of the population from May to June with the lowest value in June and July, and an increase from July to September. The age of the copepods increases from the second half of July to September. Such dynamics can relate to the life cycle of copepods when males and females reach sexual maturity. Thus, during the the vegetation period there is an increase in male copepods from 0 ind./100 in June to 5.2 ind./100 individuals. Rottger (1969), also reported year seasonal dynamics. There is a mid-summer increase in the number of female of S. gibberum.

 

Fig03

Seasonal dynamics in WSBS (pier) point.
Starfish collection depth 1 m.

Seasonal dynamics in Polovye Islands point.
Starfish collection depth 8 m.

Figure 3: Seasonal dynamics of population

 

So, the seasonal cycle of starfish populations which was observed during the 2012-2013 vegetation periods shows the lowest values in June and increase until October. The relative age of the last stage of S. gibberum and proportion of males increases.

The population index features at different depths. To analyse variability of the population index of starfish A. rubens by copepods S. gibberum depending on the depth the starfish collection was made according to the transect from the depths of 1, 5, 10 and 15 meters in WSBS (west) point.

The population index at the 1 meter depth is characterized by significant low meanings. The reason is the differences in the size structure of starfishes. The coastal zone is characterized by presence of juvenile A. rubens still not populated copepods. The settlement occurs during the starfish migration from the intertidal zone to the greater depths.

At the 1 meter depth the unfavourable hydrological conditions for the most active stages of copepods such as tidal currents, temperature and desalination can be observed. The population indexes value of the other points is not significantly different for the statistic. The highest population value is at a 10 meters depth.

The spatial dynamics population indices. Indexes were calculated by the analysis of the copepods S. gibberum population on starfish A. rubens from different parts of the collection area, which is shown in Figure 4.

The lowest value of the intensity index and the prevalence spatial dynamics can be identified near Eremeevskiy islands in 2012 year. The highest levels can be identified at the point near Polovye Islands, near v. Chernaya Rechka and in Babye Sea. The median intensity and the abundance index with high values of this coefficient are identified at the same groups of points: in Chernaya Rechka, Babye Sea, Polovye Islands.

 

Fig04

Population indices spatial dynamics in 2012 year.

Population indices spatial dynamics in 2013 year.

Figure 4: The spatial dynamics population indices